It is well-known in the art that it is important to monitor temperature of a casting mold that is operating at a high speed.
During the casting process, a typical period of temperature variation is less than ten seconds. This is because the temperature depends on a heat flux of molten steel. The heat flux may vary depending on melt temperature, mold powder characteristics and molten steel movements. Typically the molten steel flow will change during a casting process, which results in a dynamic temperature profile of the mold. If the temperature is uniform in the molten metal surface layer the solidification is uniform over the strand width. If, on the other hand, the temperature is not uniform in the molten metal surface layer the cast surface will solidify and the risk for surface cracks, inclusion entrapment and uneven solid shell will increase. Also if the solid shell is uneven there is a risk both for lower structural strength and re-melting of the solid shell that can result in a so called break-out below the mold where the shell is broken and the steel flows out causing major damage to the surrounding equipment.
Typically, the top surface of the molten steel in the mold, reveals to some extent how the molten steel flows inside the mold. As the flow speed and pattern of the molten steel is very important for the stability and homogeneity of the casting process as well as for promoting beneficial solidification and inclusion cleaning conditions, detection of the shape of the top molten steel surface is essential. A typical standing wave height of the top molten steel surface is 10 mm. In especially the later stages of a casting sequence, random clogging effects often lead to asymmetric molten steel flow patterns in the mold.
The temperature determination may be made by measuring the temperature of a copper plate of the casting mold. For measuring, determining and monitoring the temperature of the copper plate, thermocouples are mounted in holes in the copper plate. The number of the thermocouples is limited, for example up to 20 pieces due to the geometry constraints of the copper plate. Thus, the spatial resolution of measured temperatures is low.
In a recent development, optical fibers are used for measuring temperatures of a copper plate to achieve a higher resolutions of measured temperature.
US 2011/0167905 A1 describes a method comprising detecting the temperature distribution in the area of a casting level over the height of a mold by using a measuring thread and/or a measuring probe to determine the height of the casting level, where the measuring thread and/or measuring probe is detachably mounted on a copper plate of the mold and comprises fiber-optic sensors. The height of the casting level is determined from the detected temperature distribution by using an evaluation device. A further measuring probe for temperature detection may be detachably arranged in the area of the lower end of the mold.
PCT/EP2009/004901 describes another method, wherein laser light is passed through optical fibers used as sensors. Grooves are arranged made on the outer sides of copper plates of a mold. The optical fibers are located in these grooves. The fibers have a meandering arrangement in the grooves. At least two fibers are arranged in each groove. The grooves are located between cooling channels on the outside of the plates. The fibers are arranged in the fixed side, the detachable side and preferably in both narrow sides of the mold.